Amplifiers are commonly used in electronic applications. One example of the use of an amplifier is in a read channel of a hard disk drive. A read channel of a hard disk drive receives an analog signal from magnetic media of a hard disk drive and converts the analog signal into a digital form for processing by a computer. A particular type of amplifier is a programmable gain amplifier. The gain of a programmable gain amplifier is adjustable. A programmable gain amplifier may be particularly useful in the read channel of a hard disk drive because the magnitude of analog signals read from a magnetic media may vary with type of drive. Therefore, a programmable gain amplifier facilitates amplification of these varying magnitudes to appropriate levels.
In some applications, it is desirable to have a programmable gain amplifier that requires only CMOS active elements. Because of the widespread use of CMOS technology, the manufacture of CMOS devices is relatively inexpensive. In addition, the use of only CMOS devices allows easy transferability to advancing technologies incorporating smaller and smaller designs. Furthermore, the avoidance of passive elements, such as resistors or capacitors, reduces the size required to implement these circuit elements.
Because a wide range of frequencies is required in hard disk drive applications, a programmable gain amplifier for use in such an application requires a wide bandwidth. Traditional operational amplifiers cannot accommodate a wide bandwidth over a range of gains. It is also desirable to produce a programmable gain amplifier that can operate at low voltage to accommodate low voltage technology.